With reference to FIG. 14, an operation when a mobile station UE having established an RRC connection #1 in a cell #1 detects RLF (Radio Link Failure) in a mobile communication system of the LTE (Long Term Evolution) scheme defined in the 3GPP will be explained.
As illustrated in FIG. 14, in the state in which the RRC connection #1 is established between the mobile station UE and a radio base station eNB#1 and an S1 connection #1 is established between the radio base station eNB#1 and a mobile switching center MME, if the mobile station UE detects the RLF (Radio Link Failure) in step S5001, the mobile station UE performs a cell selection process in step S5002.
In step S5003, the mobile station UE transmits an “RRC Connection Re-establishment Request” to a radio base station eNB#2 managing a cell #2 selected by the cell selection process.
When the radio base station eNB#2 stores context information (UE context) of the mobile station UE, which corresponds to “Physical Cell Identity”, “C-RNTI”, and “shortMAC-I” included in the received “RRC Connection Re-establishment Request” in step S5004, the radio base station eNB#2 transmits an “RRC Connection Re-establishment” to the mobile station UE in step S5005.
In step S5006, the mobile station UE transmits an “RRC Connection Re-establishment Complete” to the radio base station eNB#2.
The radio base station eNB#2 transmits an “S1 Path Switch” to the mobile switching center MME in step S5007, and transmits an “RRC Connection Reconfiguration” to the mobile station UE in step S5008.
The mobile station UE transmits an “RRC Connection Reconfiguration Complete” to the radio base station eNB#2 in step S5009, and the mobile switching center MME transmits an “S1 Path Switch Ack” to the radio base station eNB#2 in step S5010.
As a consequence, the RRC connection #1 is switched to an RRC connection #2 and the S1 connection #1 is switched to an S1 connection #2. Here, the RRC connection #2 is an RRC connection established between the mobile station UE and the radio base station eNB#2, and the S1 connection #2 is an S1 connection established between the radio base station eNB#2 and the mobile switching center MME.
However, in the mobile communication system, the mobile station UE is configured to perform a handover only for a cell under the control of a radio base station eNB storing the context information (UE context) of the mobile station UE.
Therefore, there is a problem that when the above-mentioned radio base station eNB#2 does not store the context information of the mobile station UE, the above-mentioned “RRC Connection Re-establishment” may be rejected, and the mobile station UE may not establish the RRC connection #2 with the radio base station eNB#2 managing the cell #2 selected by the cell selection process.
Therefore, the present invention is intended to overcome the above-described problems. An object thereof is to provide a mobile communication method of enabling connection re-establishment (reconnection) with a radio base station not storing the context information of a mobile station, and a radio base station therefor.